This invention relates to wireless communications, and more specifically to adaptive methods for multiple user access in a dynamic wireless communications network.
There is growing demand for high speed access to communication networks to support data, voice, and multimedia services. In addition to services based on physical connectivity through wire or fiber, there is increasing interest in the use of wireless communication networks. Wireless communication networks offer certain economies and flexibility not available in wired networks. These include reduced time and cost for installation and maintenance.
In wireless communication networks, multiple users share the same communication medium at the same time. Because the spectrum is limited, it is important to use it efficiently in order to accommodate the needs of all users desiring access within a reasonable time. The spectral and temporal limitations lead to problems with radio interference among users transmitting at the same time.
The use of multiple antennas is known to enhance the performance and the capacity of wireless communications networks. Most systems that exploit the spatial properties of wireless communication links use multiple antennas with fixed beams that enhance a given spatial sector, thereby reducing interference from outside that sector. Additional performance enhancements can be achieved using adaptive antenna arrays. For example, an adaptive array can place nulls in the direction of specific interferes, such as from other users transmitting in the same frequency channel, and can enhance the signal of interest. However, current techniques are generally unsuitable for use in data networks where data are transmitted in discrete packets. Most of the techniques currently suggested adapt slowly and are unsuitable for point-to-multipoint topologies where users and their characteristics are constantly changing.
In a packet-switched network, data transfer between nodes, for example, between a given user and a base station in a wireless network, is typically bursty, requiring high data rates for short periods of time. Preferably, a network should exploit the silent periods associated with one user to service other users in the network. Furthermore, spectrum limitations, spectrum assignment to users in the network should be dynamic to accommodate changing bandwidth requirements and user loads. Existing methods for packet-radio systems typically suffer because of a lack of flexibility in managing resources as users enter and leave the system and as the flow of data changes.